Fossil travertine system and its palaeofluid provenance, migration and evolution through time: Example from the geothermal area of Acquasanta Terme (Central Italy)

Abstract

The geothermal area of Acquasanta Terme has often been studied for its active and fossil travertine deposits to elucidate fluid origin, geodynamic and hydrological setting. Even though present-day thermal springs are usually used to obtain most information, the three travertine terraces bordering the Tronto river contain a plethora of information. A combination of elemental and isotope analyses (δ 18 O, δ 13 C and 87 Sr/ 86 Sr-ratio), fluid inclusion microthermometry and U-Th dating is used to verify the hydrogeology and its timing. These analyses point out two fluid reservoirs with distinctly different fluids, one with low salinity of 0.7 wt% NaCl eq. and another with 28.5 wt% NaCl eq., which corresponds to the fluid composition of present-day spring fluids. Furthermore, it is demonstrated that geothermal sources were intermittently active in the past 221 ka mainly during uneven-numbered marine isotope stages, which are related to humid, interglacial periods and resulted in three different travertine terraces around 210.5, 126.5, and 36.5 ka. Accordingly, an uplift rate for this area could be estimated at around 1 mm/ka. The fluids were tapped at a depth of approximately 3 km in the tectonized, cataclastic fraction of the Triassic Anidriti di Burano Formation, the Calcare Cavernoso Formation and are originally meteoric based on geochemical evidence of a uniform 87 Sr/ 86 Sr-ratio of 0.707914 ± 0.00019 and a δ 18 Oaragonite value of -11.90 ± 0.34 ‰, which has been depressed by elevated precipitation temperatures between 22.2 and 50 °C. The characterization and dating of fossil travertine deposits gives valuable data providing insights in long-term fluid flow and orogenic uplift rates, adding valuable information to present-day spring fluid characterization.

3D reconstruction of the Lapis Tiburtinus (Tivoli, Central Italy): The control of climatic and sea‐level changes on travertine deposition

“…(2017), addressing the few square kilometre wide travertine succession of Acquasanta Terme (Central Italy), recognized two travertine aprons consisting of four aggradational‐progradational units, which were separated by erosional unconformities produced by events of non‐deposition and erosion, due to temporary interruptions of vent activity, shifts of the vent location and/or deviation of the flow directions. Also in this case, travertine geometries were linked to local topographic gradients, location and morphology of the hydrothermal vents, rates and chemistry of thermal water discharge, influenced by the substrate rocks as well as tectonic and climatic regime (Janssens et al., 2020).…”

Fissure Ridges: A Reappraisal of Faulting and Travertine Deposition (Travitonics)

“…The results suggest that the events recorded in Ca-carbonate veins indicate an epicenter with a distance of <200 km and high-intensity (I > VI) paleoearthquakes; thus, this tool has advantages over traditional paleoseismological methods for the understanding of long-term earthquake behavior. In this view, it should be possible to use age determination to reconstruct the seismicity and its recurrence [23,65,100], the fault dilatation rate [82], the age of a fault [36,65,112,116], an assessment of the slip rate [124], and relationships between faulting and fluid properties in geothermal fields [2,13,35,86,94,132,[151][152][153][154].…”

Travertine crystal growth ripples record the hydraulic history of ancient Rome’s Anio Novus aqueduct

“…Where water has sufficiently high supersaturated concentrations of dissolved minerals (hard water), it precipitates deposits composed of calcium carbonate (CaCO 3 ) limestone called travertine 2 , 3 within water transport and storage systems. In the process, these travertine deposits preserve a record of the complexly intertwined physical, chemical, and biological processes that have influenced their deposition 2 – 5 . Travertine deposited during the operation of historical aqueducts has recorded changes in human activity and climate in Europe and the Middle East 6 – 15 , Pre-Columbian North America 16 , Central Asia 17 and Australia 18 .…”

“…This terminology confirms that the travertine ripple morphologies form from a process of constructional crystal growth directly from the flowing aqueduct water. Furthermore, this terminology reflects the distinctly different typology of travertine crystallized from complex physical, chemical, and biological mechanisms 2 – 5 , which is a fundamentally different process from the fluid mechanics controlling sedimentary transport ripple formation 28 . At the same time, the nomenclature “travertine crystal growth ripples” recognizes that gravity-driven, open-channel turbulent flow is also influential in convective diffusion during travertine CaCO 3 crystal precipitation 33 .…”